Efforts have been made relating to the syntheses of nano-structured materials. In particular, efforts have been made to synthesize nanoparticles of various metals, metal oxides and semiconductors. Some syntheses have been successful, but have required large numbers of reaction stages and/or complex preparation conditions. For example, according to some synthetic techniques, size, shape and dispersity of nanoparticles are controlled by conducting decompositions of organic-metal precursors in high temperature solvents in the presence of high concentrations of surfactants.
For some systems, such as the Pt/Fe or Pt/Co alloy systems, however, obtaining crystalline phases is essential to preparation of nanoparticles. Unfortunately, to affect phase transfer in such systems, precursors must be heated to extremely high temperatures—temperatures that can not be sustained by organic solvents conventionally used in nanoparticle synthesis. Although it is feasible that phase conversion could be achieved by conducting a solid-state reaction, the aggregation of particles and the loss of capping layers that are by-products of such solid-state reactions greatly limit the potential applications of resulting particles.
Recently, research relating to ionic liquids has made it possible to use such ionic liquids in various applications. Compared with the conventional solvents, ionic liquids are nonvolatile, non-flammable and thermally stable. These features make ionic solvents desirable, for example, by improving safety during use and reducing environmental hazards relating to their disposal.
Ionic liquids can include a variety of cations and anions. With respect to nanoparticle synthesis, this variety potentially makes it possible to select a solvent in which a particular precursor has greater solubility in comparison to the solubility of that precursor in conventional solvents. As a result, greater tunability with respect to the final nanoparticle product can be achieved.
Some progress has been made in synthesizing nanoparticles using ionic liquids. However, this progress has been limited with respect to the types of nanoparticles that have be made and the ease with which the nanoparticles can be separated from other reaction products, thus limiting the practical applicability of the known approaches. Also, the cost of ionic liquids can be prohibitively high, so procedures for recycling ionic liquids after use could increase the practical applicability of those liquids.